The present invention relates to reaction chambers used for processing semiconductor substrates, such as integrated circuit wafers, and specifically to improvements in the gas distribution system used in these reaction chambers.
Semiconductor processing includes deposition processes such as chemical vapor deposition (CVD) of metal, dielectric and semiconducting materials, etching of such layers, ashing of photoresist masking layers, etc. In the case of etching, plasma etching is conventionally used to etch metal, dielectric and semiconducting materials. A parallel plate plasma reactor typically includes a gas chamber including one or more baffles, a showerhead electrode through which etching gas passes, a pedestal supporting the silicon wafer on a bottom electrode, an RF power source, and a gas injection source for supplying gas to the gas chamber. Gas is ionized by the electrode to form plasma and the plasma etches the wafer supported below the showerhead electrode.
Showerhead electrodes for plasma processing of semiconductor substrates are disclosed in commonly assigned U.S. Pat. Nos. 5,074,456; 5,472,565; 5,534,751; and 5,569,356. Other showerhead electrode gas distribution systems are disclosed in U.S. Pat. Nos. 4,209,357; 4,263,088; 4,270,999; 4,297,162; 4,534,816; 4,579,618; 4,590,042; 4,593,540; 4,612,077; 4,780,169; 4,854,263; 5,006,220; 5,134,965; 5,494,713; 5,529,657; 5,593,540; 5,595,627; 5,614,055; 5,716,485; 5,746,875 and 5,888,907.
A common requirement in integrated circuit fabrication is the etching of openings such as contacts and vias in dielectric materials. The dielectric materials include doped silicon oxide such as fluorinated silicon oxide (FSG), undoped silicon oxide such as silicon dioxide, silicate glasses such as boron phosphate silicate glass (BPSG) and phosphate silicate glass (PSG), doped or undoped thermally grown silicon oxide, doped or undoped TEOS deposited silicon oxide, etc. The dielectric dopants include boron, phosphorus and/or arsenic. The dielectric can overlie a conductive or semiconductive layer such as polycrystalline silicon, metals such as aluminum, copper, titanium, tungsten, molybdenum or alloys thereof, nitrides such as titanium nitride, metal silicides such as titanium silicide, cobalt silicide, tungsten silicide, molybdenum silicide, etc. A plasma etching technique, wherein a parallel plate plasma reactor is used for etching openings in silicon oxide, is disclosed in U.S. Pat. No. 5,013,398.
U.S. Pat. No. 5,736,457 describes single and dual xe2x80x9cdamascenexe2x80x9d metallization processes. In the xe2x80x9csingle damascenexe2x80x9d approach, vias and conductors are formed in separate steps wherein a metallization pattern for either conductors or vias is etched into a dielectric layer, a metal layer is filled into the etched grooves or via holes in the dielectric layer, and the excess metal is removed by chemical mechanical planarization (CMP) or by an etch back process. In the xe2x80x9cdual damascenexe2x80x9d approach, the metallization patterns for the vias and conductors are etched in a dielectric layer and the etched grooves and via openings are filled with metal in a single metal filling and excess metal removal process.
It is desirable to evenly distribute the plasma over the surface of the wafer in order to obtain uniform etching rates over the entire surface of the wafer. Current gas distribution chamber designs include multiple baffles which are optimized to uniformly distribute etching gas to achieve the desired etching effect at the wafer. However, the current baffle and showerhead electrode designs are best suited to empirical optimization for uniform gas distribution for a particular gap between the wafer and the showerhead electrode and are difficult to adjust to varying gaps between the wafer and the showerhead. In addition, conventional gas distribution designs include baffles having hundreds of openings or complex, difficult to manufacture geometries to ensure even distribution of etching gas to the backside of the showerhead electrode. When etching large, twelve-inch (300 mm) wafers, controlling the process gas to create a uniform pressure distribution across the showerhead is even more difficult. The number of openings and baffles must be increased significantly to maintain uniform distribution of the etching gas. As the number of openings in the baffles increase and the number of baffles increase, the complexity and cost to manufacture such a gas distribution apparatus increase greatly.
The present invention provides a gas distribution system which is a simple to manufacture design requiring a small number of baffle plates, while still achieving desired gas distribution delivered through a showerhead. Gas flow can be optimized for any size substrate and/or gap between the showerhead and the semiconductor substrate being processed. In addition, the present invention can improve heat transfer from a showerhead electrode to a cooled support plate, thereby creating better temperature uniformity across the electrode surface. Furthermore, the present invention can provide generally continuous electrical contact among the components of a showerhead electrode gas distribution system.
A gas distribution apparatus according to the present invention includes a support plate and a showerhead which are secured to define a gas distribution chamber. The chamber includes a baffle assembly including one or more baffle plates which can be used to achieve a desired pressure distribution across the showerhead. Multiple gas supplies provide process gas into the gas distribution chamber where the process gas flows downward through the baffle assembly and through the showerhead.
A first embodiment of the invention includes a baffle assembly having an upper baffle plate. A seal member, such as an O-ring is at an intermediate location between the upper baffle plate and the support plate. The seal member divides the space therebetween into inner and outer regions. Gas from a first gas supply directs gas into the inner region and gas from a second gas supply directs gas into the outer region. The arrangement allows different gas chemistries and/or gas pressures to be provided to the inner and outer regions. As a result, better control of gas chemistry and/or gas pressure across the substrate can be achieved by preselecting process parameters or adjusting such process parameters during processing of a substrate.
If desired, middle and/or lower baffle plates can be arranged to define three plenums. The first plenum is located between the upper and middle baffle plates. The second plenum is located between the middle and lower baffle plates, and the third plenum is located between the lower baffle plate and the showerhead. The plenums can be used to create a more uniform process gas pressure distribution across the showerhead.
In a second embodiment of the present invention the support member includes a recess in its lower side which defines the gas distribution chamber. The support member has a first gas outlet supplying a first process gas into a central area of the recess chamber and a second gas outlet supplying a second process gas into a peripheral area of the recess. Secured within the baffle chamber are an upper baffle plate and a lower baffle plate. The upper baffle plate is arranged to receive gas exclusively from the first gas supply and the lower baffle plate is arranged to receive gas exclusively from the second gas supply. A first set of gas passages in the upper baffle plate is in fluid connection with gas passages in the second baffle plate to create a set of flow-connected passages through which the first process gas passes directly from the upper baffle plate to the underside of the lower baffle plate. The second process gas flows through a second set of gas passages in the lower baffle plate to its underside adjacent the backside of the showerhead. In this arrangement, the first process gas does not mix substantially with the second process gas before flowing to the underside of the lower baffle. The space between the lower baffle and the showerhead can have spaced apart annular channels which allow the gases passing through the showerhead to be selectively controlled, e.g., to achieve uniform or nonuniform gas chemistry and/or pressure across the showerhead. Gas from both the first gas supply and the second gas supply flows through a third set of openings in the showerhead into a region spanning the substrate.